When and How Far to Move the Tibial Tuberosity in Patients With Patellar Instability

Increased TT-TG distance caused by excessive tibiofemoral rotation predicts poor clinical outcomes after tibial tubercle osteotomy in recurrent patellar dislocation

PURPOSE

To compare clinical outcome between recurrent patellar dislocation (RPD) with or without actual tibial tubercle lateralisation (TTL) after medial patellofemoral ligament reconstruction (MPFL-R) combined with tibial tubercle transfer.

METHODS

From 2015 to 2018, a total of 172 knees with RPD and a tibial tubercle-trochlear groove (TT-TG) distance of > 20 mm were treated with MPFL-R combined with tibial tubercle transfer. Patients were divided into the lateralisation group (TT-PCL > 24 mm, n = 74) and the nonlateralisation group (TT-PCL ≤ 24 mm, n = 60) based on the presence or absence of actual TTL (TT-PCL > 24 mm). Clinical outcomes were assessed postoperatively at a minimum of 2 years. Second-look arthroscopic evaluations were available for 84 knees to assess cartilage damage.

RESULTS

A total of 134 knees with a median follow-up time of 32 months were included. Tibiofemoral rotation (TFR) was significantly higher in the nonlateralisation group than in the lateralisation group (15.4° vs. 9.4°, P < 0.001). At the final follow-up, the nonlateralisation group had significantly lower Kujala (78.2 vs. 86.4, P = 0.001) and Lysholm (80.3 vs. 88.2, P = 0.003) scores than the lateralisation group. At the time of the second-look arthroscopic assessment, 38.9% of the patients in the nonlateralisation group showed cartilage worsening in the medial patellar facet that was significantly higher than that in the lateralisation group (38.9% vs. 12.5%, P = 0.015).

CONCLUSION

Patients with RPD and an increased TT-TG distance of > 20 mm but without actual tibial tubercle lateralisation benefit less from tibial tubercle transfer than patients with actual tibial tubercle lateralisation, which may be related to the significantly higher tibiofemoral rotation angle of the former.

LEVEL OF EVIDENCE

III.

Influence of Articular Geometry and Tibial Tubercle Location on Patellofemoral Kinematics and Contact Mechanics

Trochlear groove geometry and the location of the tibial tubercle, where the patellar tendon inserts, have both been associated with patellofemoral instability and can be modified surgically. Although their effects on patellofemoral biomechanics have been investigated individually, the interaction between the two is unclear. The authors' aim was to use statistical shape modeling and musculoskeletal simulation to examine the effect of patellofemoral geometry on the relationship between tibial tubercle location and patellofemoral function. A statistical shape model was used to generate new knee geometries with trochlear grooves ranging from shallow to deep. A Monte Carlo approach was used to create 750 knee models by randomly selecting a geometry and randomly translating the tibial tubercle medially/laterally and anteriorly. Each knee model was incorporated into a musculoskeletal model, and an overground walking trial was simulated. Knees with shallow trochlear geometry were more sensitive to tubercle medialization with greater changes in lateral patella position (-3.0 mm/cm medialization shallow vs -0.6 mm/cm deep) and cartilage contact pressure (-0.51 MPa/cm medialization shallow vs 0.04 MPa/cm deep). However, knees with deep trochlear geometry experienced greater increases in medial cartilage contact pressure with medialization. This modeling framework has the potential to aid in surgical decision making.

Relationship Between Lateral Patellar Stability Following Tibial Tubercle Osteotomy for Varying Patellofemoral Geometries

The geometry of the patellofemoral joint affects function and pathology. However, the impact of trochlear groove depth on treatments for patellar instability and pain is not clear. Tibial tubercle osteotomy is a common surgical intervention for patellar instability where the tibial insertion of the patellar tendon is translated to align the extensor mechanism and stabilize the joint. The aim of this work was to investigate the interaction between trochlear groove depth and patellar tendon insertion and their effect on patellar stability. Patellofemoral geometry was modified based on a statistical shape model to create knees with a range of trochlear groove depths. A Monte Carlo approach was used and 750 instances of a musculoskeletal model were generated with varying geometry and anterior and medial transfer of the patellar tendon. Stability was assessed by applying a lateral perturbation force to the patella during simulation of overground walking. In knees with deep trochlear grooves, a medialized patellar tendon increased stability. However, in knees with shallow trochlear grooves, stability was maximized for tendon insertion ~1 mm medial to its neutral location. This patellar tendon insertion also corresponded to the best alignment of the patella in the trochlear groove in these knees, indicating that good alignment may be important to maximizing stability. Anterior patellar tendon transfer had minimal effect on stability for all geometries. A better understanding of the effects of articular geometry and tubercle location on stability may aid clinicians in patient-specific surgical planning.

Double-Bundle Medial Patellofemoral Ligament Reconstruction With Allograft

Medial patellofemoral ligament (MPFL) reconstruction is the treatment of choice for recurrent patellofemoral instability. Although attention to MPFL reconstruction in the orthopaedic literature has increased dramatically in recent years, there is no clear consensus on surgical technique, graft option, or method of fixation. Nevertheless, most studies have shown improved pain scores and low rates of recurrent dislocation in patients after surgery. Despite the early success of MPFL reconstruction, complications may occur more frequently than previously appreciated and include patellar fracture, postoperative instability, and loss of flexion. This article describes our technique for double-bundle MPFL reconstruction with an allograft while highlighting certain aspects of the procedure that are critical for achieving favorable outcomes. The main advantages of the technique include strong patellar fixation with suture anchors and anatomic graft placement at the origin and insertion of the native MPFL. In our experience, this method of reconstruction has been safe, reproducible, and effective in the treatment of patients with patellar instability.

The medial patellofemoral complex

PURPOSE OF REVIEW

The purpose of this review is to describe the current understanding of the medial patellofemoral complex, including recent anatomic advances, evaluation of indications for reconstruction with concomitant pathology, and surgical reconstruction techniques.

RECENT FINDINGS

Recent advances in our understanding of MPFC anatomy have found that there are fibers that insert onto the deep quadriceps tendon as well as the patella, thus earning the name "medial patellofemoral complex" to allow for the variability in its anatomy. In MPFC reconstruction, anatomic origin and insertion points and appropriate graft length are critical to prevent overconstraint of the patellofemoral joint. The MPFC is a crucial soft tissue checkrein to lateral patellar translation, and its repair or reconstruction results in good restoration of patellofemoral stability. As our understanding of MPFC anatomy evolves, further studies are needed to apply its relevance in kinematics and surgical applications to its role in maintaining patellar stability.

Editorial Commentary: Measuring Coronal (Mal)Alignment for Patients With Patellar Instability: Tibial Tubercle-to-Trochlear Groove Versus Tibial Tubercle-to-Posterior Cruciate Ligament Distance

Excessive lateralization of the tibial tuberosity is one of the anatomic factors that contribute to lateral patellar instability, which we usually correct surgically with tibial tuberosity osteotomy. Traditionally, coronal alignment was determined clinically by measuring the Q angle, which has proven to be unreliable. Radiographic measurements of coronal alignment made using computed tomography and magnetic resonance imaging are more reliable and have become the standard for determining the need for corrective tibial tuberosity osteotomy. However, measurements of the distance between the tibial tuberosity and the trochlear groove vary substantially according to the imaging modality, knee-flexion angle, and other factors. An alternative approach is to measure the distance between the tibial tuberosity and the posterior cruciate ligament, which negates the confounding influence of the knee-flexion angle. Controversy remains as to the optimum measurement technique. It is crucial that knee surgeons understand the nuances of the technique used to measure coronal alignment so they can choose the optimum surgery to achieve the desired anatomic correction.